Abstract
This paper presents a study on Lithium-ion battery aging behaviors/patterns and related State-of-Health (SOH) indicators before presenting the development of data-driven based SOH estimators. Battery charge/discharge cycling experiments are conducted in order to obtain needed data for this work. The battery ageing behavior patterns until the battery cell reaches highly deteriorated health conditions are investigated and characterized in this paper by analyzing the aggregated battery ageing data. The observed battery ageing behavior patterns include: (1) the rate at which the battery voltage decreases during discharging increases as the battery ages, (2) the speed at which the battery terminal voltage increases during Constant Current (CC) charging increases as the battery's health deteriorates, (3) the time period for CC charging operation decreases as the battery ages, (4) the rate at which the battery current decreases during Constant Voltage (CV) charging increases as the battery ages, and (5) the speed at which the battery temperature drops during CV charging increases as the battery ages. Corresponding SOH indicators are developed to quantify these battery ageing behavior patterns for the development of SOH estimators. Deep Neural Network (DNN) is utilized to extract and model the nonlinear and complex correlation between the defined SOH indicators and SOH values of the Lithium-ion battery. Multiple DNN-based SOH estimators are developed in this paper. The SOH estimation results from different DNN-based SOH estimators indicate that the diversity of SOH indicators used for the development of SOH estimator can substantially improve the estimation performance.
Highlights
Lithium-ion battery currently has the majority of market share in the energy storage applications, especially in electric vehicles (EVs) application, because of its superior performance compared with other types of batteries
The observed battery ageing behavior patterns include: (a) the rate at which the battery voltage decreases during discharging increases as the battery ages, (b) the speed at which the battery terminal voltage increases during Constant Current (CC) charging increases as the battery’s heath deteriorates, (c) the time period for CC charging operation decreases as the battery ages, (d) the rate at which the battery current decreases during Constant Voltage (CV) charging increases as the battery ages, and (e) the speed at which the battery temperature drops during CV charging increases as the battery ages
Lithium-ion battery ageing behavior patterns or characteristics are extracted in this paper from the aggregated raw battery ageing data collected from the developed autonomous battery ageing platform
Summary
Battery voltage increasing speed during constant current charging process Battery current decreasing speed during constant voltage charging process Battery temperature decreasing speed during constant voltage charging process Battery voltage decreasing speed during discharging process The ith multiple SOH indicators based DNN SOH estimator, i = 1, 2, 3, 4 Ground truth SOH value of the ith sample Predicted SOH value for the ith sample SOH estimator utilizing single SOH indicator Δt| SOH estimator utilizing single SOH indicator |. The ith SOH indicator, where i = 1, 2, 3, 4, 5 Calibrated capacity value Nominal capacity value Original sample data Normalized data Minimum value Maximum value Voltage difference Temperature difference Time interval Time period of constant current charging process
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